Singletons

• Singleton<T>
  • lazily instantiate an instance of a concrete type
• ManualSingleton<T>
  • Instance property will not lazily instantiate. It will return null if it has not been initialized.
  • GuaranteedInstance will lazily instantiate.
    • If T is an interface type, and the interface has the [DefaultImplementationType], it will look to ManualSingleton<DefaultImplementationType>.Instance.